JP2816011B2 - Rewritable optical recording medium and recording method thereof - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a rewritable optical recording medium.

2. Description of the Related Art As a conventional rewritable optical recording medium, a so-called phase change type using a difference in optical characteristics between a crystalline state and an amorphous state of a recording film, and a difference in a Kerr rotation angle of a recording film are used. A magneto-optical type and the like are known.

Problems to be Solved by the Invention However, such a conventional technique has advantages and disadvantages in terms of the wavelength of light used, high-density recording property, power of light used, repetition characteristics, transfer rate, multilevel recording, and the like. There is a problem that there is.

The present invention provides a rewritable optical recording medium in which particles are dispersed in a medium and recording is performed by using a change in the spatial distribution of the particles in consideration of such a problem of the conventional rewritable optical recording medium. The purpose is to do so.

Means for Solving the Problems The present invention provides a mixture of particles and a medium in which the particles are dispersed, the optical properties are different, the melting point is lower than the particles, and the specific gravity of the molten state is different from the specific gravity of the particles, A rewritable optical recording medium characterized by having a configuration in which a groove of a disk substrate provided with groove-shaped tracks is filled.

Function The present invention irradiates light to melt the medium while the substrate is rotating. Because the medium has a lower melting point than the particles, the particles do not melt when the medium melts. Further, since the specific gravities are different, the particles move and are biased by the rotational centrifugal force. Thereafter, by cooling, the particles are kept in an uneven state. Since the optical characteristics are different between the medium and the particles, the recording can be reproduced.

Embodiment Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 (a) is a partially cutaway perspective view showing one embodiment of a rewritable optical recording medium according to the present invention, and FIG. 1 (b).
Is an enlarged plan view on the AB line shown in FIG. 1 (a), and FIG. 1 (c) is an enlarged sectional view on the AB line shown in FIG. 1 (a).

In FIGS. 1 (b) and 1 (c), reference numeral 1 denotes particles which are chemically stable and have a high melting point.
The particles are made of an inorganic pigment such as carbon black, or an organic pigment such as an azo-based, triphenylmethane-based, quinoline-based, anthraquinone-based, or phthalocyanine-based pigment. 2
Does not react with the particles 1 and is solid at normal temperature and has a melting point of the particles 1.
And a medium whose specific gravity in the molten state is different from that of the particles 1, such as low-melting glass, thermoplastic resin, paraffins, and fats and oils. Reference numeral 3 denotes a disk substrate provided with groove-shaped tracks 6, 4 denotes a protective layer for protecting the entire disk, and 5 denotes recording light applied to the disk. Here, the disk substrate 3 and the protective layer 4 are chemically stable, do not react with the particles 1 and the medium 2, and are made of a material having a melting point higher than that of the medium 2.

Next, a method of recording, generating and erasing the rewritable optical recording medium having such a configuration will be described.

At the time of recording, a strong recording light 5 is irradiated, and this light is absorbed by the particles 1, the medium 2, the disk substrate 3, and the protective layer 4, the temperature rises, and the medium 2 is melted. At this time, if the specific gravity of the particles 1 is larger than that of the melted medium 2, the particles 1 are biased in the outer circumferential direction, that is, in the B direction due to the centrifugal force generated by the rotation of the disk.

The rewritable optical recording medium has a disk shape and groove-shaped tracks 6 are provided on the disk. Since this disk is rotating at high speed, a strong centrifugal force is acting on each part. For example, a centrifugal force of 3553 [m / s ² ] ≒ 363 G is applied at a position 100 mm from the center of the disk rotating at 1800 rpm.

Therefore, when the medium 2 in which particles are uniformly dispersed is filled in the groove-shaped track 6 and a recording light is irradiated to a certain pit in the track 6 to melt the medium, the particle 1 is changed due to a difference in specific gravity.
Are biased toward the outer peripheral side or the inner peripheral side in the pit. When cooling is performed in this state, that is, when the recording light is removed, the recording is completed.

At the time of reproduction, it is sufficiently weaker than at the time of recording,
Is irradiated to such an extent that the light does not melt, and transmitted light or reflected light of the reproduced light is detected. When the particles 1 are biased, the number of the particles 1 interacting with light is small. Therefore, depending on the optical characteristics of the particles 1, the intensity of the transmitted light or the reflected light becomes larger or smaller than in an unrecorded state, that is, a state in which the particles 1 are uniformly dispersed.

Erasing can be performed by heating the medium 2 to a temperature at which the medium 2 is melted in a stationary state, heating the medium 2 with a heating device such as an oven, and maintaining the temperature until the particles 1 are diffused and homogeneously dispersed.

In this embodiment, the specific gravity of the particles 1 is the medium 2 in the molten state.
However, the particle 1 may be biased toward the inner circumference side, that is, the direction A.

As described above, according to this embodiment, recording can be performed even if the intensity of the recording light 5 is lower than that of a conventional rewritable optical recording medium. This is because the melting point of the medium 2 is generally lower than the melting points of the phase change type and magneto-optical type materials. Therefore,
A laser in a short wavelength region having low intensity can be used as recording light, which is advantageous for improving the recording density, and is also advantageous for high speed recording. Further, since the temperature rise during recording is small, improvement in rewriting repetition characteristics can be expected.

 Next, a second embodiment of the present invention will be described.

In the second embodiment, the particles 1 in the first embodiment are used as phosphors, and the principle of recording and erasing is the same as that of the first embodiment. The principle of reproduction and the features of the present embodiment will be described below.

At the time of reproduction, light that is sufficiently weaker than at the time of recording is used. When the reproduction light and the particles 1 act, fluorescence having a longer wavelength than the reproduction light is generated. Reproduction is performed by detecting the intensity of this fluorescence. This means that the recording state can be detected with light having a wavelength longer than the reproduction light.

Therefore, this embodiment has the following advantages.

Generally, the sensitivity of an optical sensor such as a silicon photodiode is extremely low in the ultraviolet light range. Transfer rate becomes slow. Further, it is not desirable to increase the reproduction light intensity too much because there is a risk of destroying the recording state and there is no simple light source. Therefore, if the recording state is detected with light having a wavelength longer than the reproduction light, an area where the sensitivity of the optical sensor is high can be used, and a high-quality reproduction signal can be obtained.

As described above, the present invention is advantageous for high-density recording using ultraviolet light.

 Next, a third embodiment of the present invention will be described.

The third embodiment of the present invention relates to the particle 1 according to the first embodiment.
Generates the second harmonic of the laser beam, and the principle of recording and erasing is the same as in the first embodiment.

 The principle of reproduction and the features of the present embodiment will be described below.

When a laser beam is used as the reproducing beam at the time of reproducing, the reproducing beam and the particles 1 act to generate a second harmonic which is a laser beam having a wavelength half that of the reproducing beam. Reproduction is performed by detecting the second harmonic.

Therefore, this embodiment has the following advantages.

The intensity of the second harmonic is proportional to the square of the intensity density of the laser light incident on the particle. When the laser beam is focused in a spot shape, the intensity density becomes extremely large near the center,
It becomes a so-called Gaussian distribution.

Therefore, even in the case where the particles 1 are biased, in the first and second embodiments, the light which interacted with the particles 1 partially remaining in the reproduction light spot affected the reproduction signal. Becomes extremely small. That is, since the remaining particles 1 exist only near the outer periphery of the light spot, the second harmonic generated from these particles is extremely small, so that the signal intensity difference between the recorded state and the unrecorded state increases, and the C /
N gets better.

As described above, according to the present embodiment, a good reproduced signal can be obtained.

Next, a fourth embodiment of the present invention will be described with reference to FIGS. The erasing method is exactly the same as in the first embodiment.

In this embodiment, there are N types of particles 1 in the first embodiment, and these N types of particles have different absorption wavelengths and specific gravities or coefficients of thermal expansion. Hereinafter, for simplicity, it is assumed that N = 2 and the particles (1) and (2) are described.

It is assumed that the specific gravity of the particle (1) is larger than or the same as the specific gravity of the particle (2), but the coefficient of thermal expansion of the particle (2) is larger than the coefficient of thermal expansion of the particle (1). Therefore, when the recording light is irradiated and the temperature rises and the medium 2 is melted, the moving speed due to the centrifugal force acting on the particles (1) having a large difference in specific gravity from the medium 2 becomes larger.

FIG. 2 is a diagram showing the absorbance-wavelength characteristics of the particles (1) and (2), where the horizontal axis λ is the wavelength and the vertical axis α is the absorbance. Particles (1) and (2) show the highest absorbance for light of wavelengths λ1 and λ2, respectively.

FIG. 3 corresponds to FIG. 1 (b), wherein 1 is a particle (1), 2 is a particle (2), 3 is a recording light having a low intensity,
Is a recording light having a high intensity.

In the pit irradiated with the weak recording light 3,
As shown in the figure, only the particles (1) are deviated to the outer peripheral side, that is, in the direction B, and in the pit irradiated with the recording light 4 having low intensity, both the particles (1) and (2) are deviated to the outer peripheral side. The reason is as follows.

In general, the viscosity of the medium 2 in the molten state decreases as the temperature increases. Therefore, since the pits irradiated with the weak recording light 3 have a low temperature and a high viscosity, only the particles (1) having a high moving speed are deviated to the outer peripheral side until the medium 2 is solidified. On the other hand, the pits irradiated with the high intensity light 5 have a high temperature and a low viscosity, so that the movement speed of the particles (2) increases, and the particles (2) are also deviated to the outer peripheral side before the medium 2 is solidified.

When reproducing the recorded data by using the recording light in this manner, the light including the light of λ1 and λ2 is used as the reproduction light, and the spectrum of the transmitted or reflected light is observed or
The recording state can be detected by observing the transmitted or reflected light intensity of each of the two types of light 1 and λ2 as reproduction light.

As described above, according to the present embodiment, by setting a large number of recording light intensities, multi-value recording becomes possible and a high-density recording medium can be obtained.

It is to be noted that, based on the same principle as that of the present embodiment, multi-level recording is possible even by using the phosphor used in the second and third embodiments and the particles generating the second harmonic.

Effects of the Invention As described above, according to the present invention, high-density recording with short-wavelength light, recording with low-power recording light, high repetition characteristics, high transfer rate recording, or multi-level recording can be performed. The practical effect is great.

[Brief description of the drawings]

FIG. 1 shows the first rewritable optical recording medium according to the present invention.
FIG. 2 is an overall absorbance-wavelength characteristic diagram of the fourth embodiment, and FIG. 3 is a partial plan view of the fourth embodiment. 1 ... particles, 2 ... medium, 3 ... disk substrate, 4 ...
Protective layer, 5 ... Recording light.

────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Katsuya Wakita 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (58) Field surveyed (Int. Cl. ⁶ , DB name) G11B 7/24 522

Claims (5)

(57) [Claims] A groove-shaped track is provided with a mixture of particles and a medium in which the particles are dispersed and have different optical properties, a melting point lower than that of the particles, and a specific gravity in a molten state different from that of the particles. A rewritable optical recording medium characterized by having a structure filled in a groove of a disk substrate. 2. The recording method according to claim 1, wherein the medium is irradiated with light while the substrate is rotating, the medium is melted, and the particles are moved and biased by centrifugal force and then cooled to record. Recording method of a rewritable optical recording medium. 3. The rewritable optical recording medium according to claim 1, wherein the particles are made of a material that generates fluorescence. 4. The rewritable optical recording medium according to claim 1, wherein the particles are made of a material that generates a second harmonic of the irradiated laser light. 5. The rewritable optical recording medium according to claim 1, comprising N kinds of said particles having different absorption wavelengths and different specific gravities or thermal expansion coefficients.